Decoupling fast reduction from selective oxidation via bidirectional charge steering in MXene-UPDI/ZnIn₂S₄...

Nanoscale control of charge-flow pathways can enable multifunctional photocatalysis by decoupling fast reduction from selective oxidation. Here, we report an MXene-bridged urea-modified perylene diimide polymer (UPDI)/ZnIn₂S₄ ternary photocatalyst, denoted as UPMZ-50 (UPDI/MXene/ZnIn₂S₄ containing 50 wt% ZnIn₂S₄) that realizes a bidirectional dual-Schottky charge-transfer topology. Structural and electronic characterizations reveal that metallic MXene forms back-to-back Schottky junctions with both UPDI and ZnIn₂S₄. This configuration generates two oppositely oriented interfacial electric fields at the semiconductor/MXene contacts, which direct photogenerated electrons from both semiconductors onto the MXene nanosheets. Consequently, this architecture separates electron-rich reduction domains on MXene from hole-rich oxidation regions on the semiconductors. This dual-Schottky architecture suppresses charge recombination and enables stable multifunctional photocatalysis. Under optimized conditions, UPMZ-50 delivers efficient H₂O₂ production (987 μmol·g^-1·h^-1, 76.3% selectivity) and 92.4% tetracycline (TC) removal, while also exhibiting an H₂ evolution rate of 10.0 mmol g^-1·h^-1 as a benchmark for reduction performance. Mechanistic investigations identify superoxide (·O₂^-) as the dominant reactive oxygen species (ROS) and a key intermediate for H₂O₂ synthesis. The in situ generated H₂O₂ is subsequently activated to yield ·OH, and together, these ROS promote TC degradation. These findings highlight MXene-based dual-Schottky heterojunctions as a versatile strategy for tuning charge-flow regulation. This work offers a transferable blueprint for decoupling high-rate reduction from ROS-driven selective oxidation, thereby bridging the gap between efficient solar-fuel production and environmental decontamination.